The present invention relates to electronic velocimeters and in particular to velocimeters employed to measure the muzzle velocity of a projectile.
The muzzle velocity of a projectile is a significant operating parameter of a weapon. Knowing the angle of elevation and muzzle velocity, the trajectory of a shell can be readily computed. A measurement of muzzle velocity can also be dispatched to an automatic gun control system to adjust gun elevation in response to variations in the muzzle velocity. In addition, a measurement of muzzle velocity can be a useful diagnostic tool for assessing barrel wear or projectile quality.
Known velocimeters have employed a magnetized projectile which is fired through a pair of spaced coils. Besides the special projectile which is required, the spacing between coils enlarges the device, making it cumbersome. Other known velocimeters substitute a light source and photocell for each of the above mentioned coils. While the latter system does not require a special projectile, the requisite spacing between photocells is still cumbersome. Microwave interferometers may be employed to measure muzzle velocity, however, such systems are relatively complicated and costly. In addition care must be taken to direct a microwave beam axially into the gun tube. This approach requires a system of reflectors and its performance is degraded by pointed projectiles which do not reflect microwave energy well. Another known velocimeter employs a spaced pair of strain or pressure gauges mounted on the gun tube which sense the strain caused by the passing projectile. This system is prone to false readings caused by acoustical or vibrational shock waves caused at the instant of firing. Also the strain on the gun tube lags the passage of the projectile to an extent which degrades accuracy.
The present invention measures velocity by measuring the transit time of a projectile through a coil. Since a pair of spaced coils is not required a simple and compact measurement system is provided which may be conveniently mounted on the muzzle, in some embodiments.